The invention relates to a change-speed gearbox in with three epicyclic partial gear trains, each having an inner and an outer co-axial gearwheel and each having at least one planetary gearwheel in toothed engagement with the two co-axial gearwheels and supported on a planet carrier, and in which in input shaft is directly connected to one co-axial gearwheel of the input-end partial gear train and is connected to one co-axial gearwheel of the output-end partial gear train by means of a drive clutch, and in which, in the output-end partial gear train, the planet carrier is continuously connected to an output shaft and the other co-axial gearwheel is connected to a forward gear brake, and in which, in the input-end partial gear train, also the other co-axial gearwheel and the planet carrier continuously connected to one co-axial gearwheel of the third partial gear train can be fixed so that it cannot rotate relative to the input shaft by engaging in a lock-up clutch, and in which, in the third partial gear train, the planet carrier is both continuously connected to the co-axial gearwheel of the output-end partial gear train, which co-axial gearwheel can be connected to the input shaft, and is connected to a reverse gear brake and the other co-axial gearwheel has a drive connection with the co-axial gearwheel, connected to the forward gear brake, of the output-end partial gear train and can be put into an opposite direction of rotation of the input shaft by engaging the reverse gear brake, and in which, in a significant forward gear, both the drive clutch connected to the input shaft and the forward gear brake connected to one co-axial gearwheel of the output-end partial gear train are engaged and, in consequence, the gear transmission ratio is equal to the transmission ratio of the output-end partial gear train.
In a known change-speed gearbox of the type mentioned above (U.S. Pat. No. 3,863,524, FIG. 6), the inner co-axial gearwheel of the output-end partial gear train and the inner co-axial gearwheel of third partial gear train, used as the reversing train in reverse gear, are rigidly connected together by means of a coupling shaft connected to the forward gear brake in accordance with the known Simpson design. In the significant forward gear, in this case in the third gear, the co-axial gearwheel, connected to the planet carrier of the input-end partial gear train, of the third partial gear train is consequently driven with a step-up ratio relative to the input shaft although no torque is being transmitted to the output shaft in this power path. The fact that in the input-end partial gear train, the rotational speed of the planet carrier--which is higher than the rotational speed of the input shaft--has a further step-up transmission ratio relative to the rotational speed of the second co-axial gearwheel is particularly disadvantageous in this case.
From DE 32 48 350 C2, a change-speed gearbox of a different generic type with four epicyclic partial gear trains is known with, in each case, an inner and an outer co-axial gearwheel and with at least one planetary gearwheel, which is supported on a planet carrier and is in engagement with both co-axial gearwheels. In this change-speed gearbox, the fourth partial gear train alone forms the gear transmission ratio in a gear designed as the overdrive gear. For this purpose, it can be connected--when the input shaft is connected to the input-end partial gear train by means of two engaged drive clutches and the input-end partial gear train rotates, in consequence, as a block--to the input shaft by means of is planet carrier via a fourth drive clutch and the input-end partial gear train located in series in the force path. The overdrive gear transmission ratio is then formed in such a way that in the fourth partial gear train, the inner co-axial gearwheel is brought to rest by a gear brake so that the planet carrier connected to the input shaft drives the outer co-axial gearwheel with a step-up ratio, which outer co-axial gearwheel is connected to the output shaft via the planet carrier of the output and partial gear train.
In this known change-speed gearbox, the gear brake connected to the inner co-axial gearwheel of the fourth partial gear train used as the overdrive gear transmission ratio is also used to form the gear transmission ratio of the significant forward gear, in which the gear transmission ratio is equal to the transmission ratio of the output-end partial gear train. For this purpose, the inner co-axial gearwheel, which is connected to the gear brake, of the fourth partial gear train is connected to the inner co-axial gearwheel of the output-end partial gear train by means of a third drive clutch which, together with the gear brake, is engaged in the significant forward gear in which the outer co-axial gearwheel, which is in continuous drive connection with the coupling shaft of the input-end partial gear train, is driven by the input shaft when both drive clutches of the input-end partial gear train are engaged.
In this known change-speed gearbox, the output-end partial gear train does not participate in the torque conversion in the forward gear designed as the overdrive gear, and its inner co-axial gearwheel, due to the disengaged condition of the third drive clutch, rotates as a free gear element with a rotational speed which has a further step-up ratio relative to the rotational speed of the output shaft, which already has a step-up ratio.
The object on which the invention is based consists essentially in creating a change-speed gearbox which has three epicyclic partial gear trains and which, as far as possible, in all gears avoids the possibility of gear elements not participating in the torque transmission having substantially higher rotational speeds than the input shaft.
The object explained is achieved in an advantageous manner, in accordance with the invention, by providing an arrangement wherein a second drive clutch is used as the drive connection between the co-axial gearwheel which can be put into the opposite direction of rotation, of the third partial gear train and the co-axial gearwheel, connected to the forward gear brake, of the output-end partial gear train, and wherein the significant forward gear, the lock-up clutch of the input-end partial gear train is additionally engaged but the second drive clutch, is on the contrary, disengaged.
In the change-speed gearbox according to the invention, the second co-axial gearwheel of the third partial gear train, which is released in its drive connection from the second co-axial gearwheel of the output-end partial gear train, rotates as a free gear element in the significant forward gear and, in the third partial gear train, both the planet carrier (due to the engaged drive clutch) and the first co-axial gearwheel (due to the engaged lock-up clutch of the input-end partial gear train) have the rotational speed of the input shaft. In consequence, the third partial gear train and also the input-end partial gear train each respectively rotate as a block so that no higher rotational speeds can occur in these partial gear trains not participating in the torque transmission.
In the known change-speed gearbox forming the generic type, the direct fourth gear is the highest gear whereas, in the significant third gear, the gear transmission ratio is maintained by the transmission ratio of the output-end partial gear train alone.
In order to obtain a fifth gear in the known change-speed gearbox forming the generic type, either a fourth epicyclic partial gear train is provided or a second coupling shaft is provided between the input-end partial gear train, on the one hand, and the two other partial gear trains, on the other.
In the change-speed gearbox according to the invention, a fifth gear is made possible by means of an arrangement wherein in a further forward gear, the two drive clutches and and also a gear brake connected to the other co-axial gearwheel of the input-end partial gear train are engaged.